1. Field of the Invention
This invention relates to a power transmission mechanism, and more particularly to a programmable power transmission mechanism, which includes a small-size servomotor that cooperates with a power source to rotate a rotating shaft in two directions.
2. Description of the Related Art
Due to the need for automation of mechanical devices, some power sources, such as electrical motors, hydraulic motors, hydraulic cylinders, pneumatic cylinders, etc, are used in a bulky machine that requires a comparatively large power output, e.g. a plastic injection molding machine or a press machine. However, electrical motors or hydraulic motors are capable of unidirectional rotation only. Although a large-size servomotor can offer a large power output to rotate an object in two rotational directions, it is relatively expensive.
An object of this invention is to provide a power transmission mechanism, which includes a small-size programmable servomotor that cooperates with a power source so as to transmit torque from the power source, thereby rotating a rotating shaft in two directions.
According to this invention, a programmable power transmission mechanism includes first and second torque output units, each of which has a primary driving gear. When a power source rotates an input gear in one direction, the two primary driving gears rotate in two opposite directions. At this time, a motor shaft of a small-size servomotor can rotate in a first direction so that torque is transmitted from the input gear to a rotating shaft via the first torque output unit. Alternatively, the motor shaft can rotate in a second direction that is opposite to the first direction so that torque is transmitted from the input gear to the rotating shaft via the second torque output unit. As such, the first and second torque output units can drive the rotating shaft to rotate in two opposite directions.